1. Field of the Invention
The present invention is directed to an x-ray tube of the type having an anode and a cathode assembly that are situated in an evacuated housing provided with a beam exit window, with the anode at a common, first potential and the cathode assembly at a second potential that is negative in comparison to the first potential.
2. Description of the Prior Art
In x-ray tubes of the above type, there is a risk that secondary electrons emitted from the anode will be incident on the beam exit window and will excessively heat the beam exit window.
In order to prevent this, the space situated between anode and cathode in an x-ray tube disclosed by U.S. Pat. No. 3,549,931 is surrounded by a shield provided with a beam passage opening. This solution, however, involves substantial structural outlay.
In an x-ray tube disclosed in European Application 0 369 529, a bead is applied to the cathode, which is intended to prevent secondary electrons from proceeding to the beam exit window. The effect of this bead is, however, only slight.
In an x-ray tube disclosed in German PS 619 748, the glow cathode is arranged in the immediate proximity of the inner side of the beam exit window and the correspondingly fashioned anode is arranged in the immediate proximity of the cathode and beam exit window in order to assure that substantially all electrons emanating from the cathode are incident on the active surface of the anode. Such a structure is unsuitable for modern x-ray tubes because of the high voltages employed; the proximity of the above components does not afford sufficient dielectric strength to prevent arcing.